1. Field of the Invention
The present invention relates to power supplies, and more particularly, to a method and apparatus of providing a power supply system having a redundant power supply switchover circuit, which maintains a remotely regulated output voltage when the power supply system switches over from the primary power supply to the secondary power supply. The present invention is particularly applicable to in-flight entertainment systems.
2. Description of the Related Art
Over the past few decades, commercial aircraft has become a necessary mode of travel for personal and business reasons. To improve passenger comfort, commercial aircraft typically offer a number of entertainment activities that can be enjoyed by the passenger, such as video games, movies and various selections of music. In addition, various electronic systems for supporting communications and/or other in-flight functions are provided.
In such in-flight entertainment systems, loss of power typically results in the interruption of the in-flight entertainment services. To avoid such interruption in services, backup or secondary power supplies are generally provided. Thus, if one power supply fails, the redundancy in the power supply system allows the other power supply to continue to supply power to the electronic components in the electronics system without interruption in service.
There are typically two types of redundant power supply systems. In the first, which is generally known as the cold standby mode, the backup or secondary power supply is not energized. The secondary power supply is energized only when the primary or main power supply fails. One disadvantage in using such a cold standby mode includes the temporary unavailability of services, since the power supply system requires a period of time to switch over to the secondary power supply. The advantage of such a cold standby mode includes extended life for the secondary power supply.
In the second type of redundant power supply system, generally known as the hot standby mode, both the primary and the secondary power supplies are energized at the same time. As a result, both the primary and the secondary power supplies contribute power to the load. In the event that the primary power supply fails, the secondary power supply will immediately become available to supply power to the load. The advantage of such a hot standby mode includes the provision of uninterrupted services while the disadvantage includes reduced life of the secondary power supply.
In most in-flight entertainment systems, the provision of uninterrupted services is a highly desirable feature. As a result, the hot standby mode is typically used in these systems despite the reduced life expectancy of the secondary power supply. A typical configuration for providing such a redundancy in power supply systems using a hot standby mode, is to OR the outputs of the power supplies 12 and 14 through a pair of diodes 16 and 18, as shown in FIG. 1. The diodes 16 and 18 are connected so that the cathode (i.e. positive terminal) of each diode 16 or 18 is connected to one terminal of the load 20, while the anode (i.e. negative terminal) of each diode 16 or 18 is connected to the positive output terminal of each of the power supplies 12 and 14. The other terminal of the load 20 is connected to the negative output terminal of each of the power supplies 12 and 14. In this configuration, either power supply 12 or 14 is capable of delivering full power to the load 20. Remote sense lines 22 and 24 coupled to each power supply 12 and 14 respectively, allow each power supply 12 and 14 to regulate the voltage across the load 20 and account for the voltage drop across the diodes 16 and 18.
A significant problem with this configuration, as discussed earlier, is that, under normal operating conditions, the load 20 draws power from both power supplies 12 and 14. Over an extended period of time, this subjects both power supplies 12 and 14 to operational stress. As a result, either or both of the power supplies 12 and/or 14 have to be replaced frequently. In addition, since both power supplies 12 and 4 are equally stressed, the possibility of a single failure point, that is, the failure of both power supplies 12 and 14, increases, thus reducing the reliability of the electronics system which utilizes the power supplies 12 and 14.
Accordingly, there is a need in the technology for an apparatus and method for providing a redundant power supply redundancy which offers the advantages of both a hot standby mode and a cold standby mode, such as the provision of uninterrupted services, while imposing little stress on the secondary power supply, so that the life expectancy of the secondary power supply will be extended. There is also a need in the technology for a redundant power supply which provides backup power in a very short period of time, while ensuring that power supply voltage fluctuations are within the operating range of the load during the switchover period.